Bone engaging prosthesis

ABSTRACT

A bone prosthesis is provided which includes an implantable elongate stem member having a bore extending therethrough. The stem member has a proximal end and a distal end with at least one slot formed in the distal end. The slot extends along at least a portion of the stem member, in a longitudinal direction, from the distal end towards the proximal end to form at least two tines at the distal end of the stem. A bolt member is disposed within the bore of the stem member and has a proximal end and a distal end, wherein at least a portion of the bolt member proximate the distal end is threaded. An expander nut is disposed between the tines and is threadably matable with the distal end of the bolt member such that rotation of the bolt member in a first direction is effective to draw the expander nut towards the proximal end of the stem member to separate the tines at the distal end of the stem member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/137,249,filed Aug. 20, 1998, now U.S. Pat. No. 6,355,069, and entitled “BONEENGAGING PROSTHESIS.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

FIELD OF THE INVENTION

The invention relates to the field of implantable articles. Moreparticularly, the invention relates to a prosthesis system which has anexpandable stem region to secure the prosthesis system within a longbone.

BACKGROUND OF THE INVENTION

Joint replacement surgery is quite common and enables many individualsto function normally when otherwise it would not be possible to do so.Artificial joints are normally composed of metallic and/or ceramiccomponents that are fixed to existing bone closest to the joint beingreplaced.

Artificial hip joints, for example, include several components. Afemoral component of an artificial hip includes an elongate stem orshaft at its distal end that is affixed within the medullary canal ofthe femur. A proximal end of the stem has a neck region which includes atrunnion, to which is attached a femoral head. The acetabular shell is aseparate component of an artificial hip joint that is affixed withinexisting bone such as the acetabulum. The acetabular shell oftenincludes a cup-like liner that receives the femoral head.

Typically, for a hip joint, the elongate stem or shaft portion of theprosthesis is implanted in the medullary canal of the femur. However,many times the femur or other long bone where the stem portion is to besecured can be in a damaged or weakened condition insufficient tosupport the prosthesis. In such cases, it may be necessary to use a stemhaving a length that extends beyond the isthmus or narrow portion of thebone.

However, extending the prosthesis beyond the isthmus poses a conflictingproblem since the supporting bone beyond the isthmus both widens and candiverge in more than one plane. A prosthesis stem narrow enough to passthrough the isthmus may not have sufficient dimensions to provide asecure fit beyond the isthmus where the supporting cortical bone widensor diverges in more than one plane.

Thus it would be desirable to have a prosthesis system that has a strongand effective support for structurally unsound long bone while stillbeing able to pass through the narrow portion of the long bone.

SUMMARY OF THE INVENTION

The invention provides a modular joint prosthesis which includes animplantable elongate stem member having a bore extending therethrough.The stem member has a proximal end and a distal end with at least onelongitudinally oriented slot formed in the distal end. The slot islongitudinally formed in at least a portion of the stem member, and itextends from the distal end towards the proximal end to form at leasttwo tines at the distal end of the stem.

The prosthesis also includes a bolt member that is disposable within thebore of the stem member. The bolt member has a proximal end and a distalend, at least a portion of which is threaded.

An expander nut is disposed between the tines of the prosthesis and itis threadably matable with the distal end of the bolt member. Therotation of the bolt member in a first direction is effective to drawthe expander nut towards the proximal end of the stem member to separatethe tines, thus expanding the distal end of the stem member. Theexpander nut may have more than one diameter to spread the tines todifferent diameters and alternatively, the tines may be provided withvarying thicknesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a joint prothesis of the presentinvention.

FIG. 2 is an exploded perspective view of the joint prothesis of FIG. 1.

FIG. 3 is a side sectional view of the joint prothesis of FIG. 1 in anexpanded condition.

FIG. 4A is a detailed sectional view of the distal portion of the jointprothesis of the present invention in an unexpanded condition.

FIG. 4B is a detailed sectional view of the distal portion of the jointprothesis of the present invention in an expanded condition.

FIG. 5A is a bottom view of the joint prosthesis of FIG. 4A in anunexpanded condition.

FIG. 5B is a bottom view of the joint prosthesis of FIG. 4B in anexpanded condition.

FIG. 6A is a bottom view of another embodiment of the joint prothesis inan unexpanded condition.

FIG. 6B is a bottom view of another embodiment of the joint prosthesisin an expanded condition.

FIG. 7 is a bottom view of another embodiment of a joint prosthesishaving expandable tine members of varying thicknesses.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 3, a joint prothesis component system 10 isprovided. The system 10 includes prosthesis 11 with a collar region 12,an elongated stem region 16, a bolt member 18 and an expander nut 20. Inthe embodiment illustrated and described herein, the joint prosthesiscomponents are shown as femoral components of a hip joint prosthesissystem. It is understood, however, that the invention applies tocomponents of other prosthesis systems which require the mounting of aprosthesis to a long bone.

The collar region 12 has a main body 22 which includes a superiorsurface 24 and an inferior surface 26. A recessed mounting cavity 30which communicates with bore 34, is provided on the superior surface 24of the collar 12. The cavity 30 includes a retaining shoulder 32 thatprevents a bolt head 50 from sliding further into the stem member 16.Extending from the superior surface 24 is a joint motion surface 14having a neck portion 15 which has a standard, Morse type taper to allowfixing of a spherical ball, not shown, to the prosthesis. The sphericalball may be either positioned in an acetabular cup, not shown, in thetotal hip prosthesis or placed directly into the acetabulum to form anendoprosthesis.

Extending distally from the inferior mounting surface 26 of collar 12 isan elongate stem region 16 having a longitudinal axis 48. Asillustrated, the stem member 16 has a substantially circular crosssection but may also be elliptical, oval, spherical or any othersuitable shape to conform to the bone in which the prosthesis is to beimplanted. Stem member 16 has a proximal end 40 and a distal end 42 withat least one longitudinal slot 44 formed in the distal end 42. The slot44 extends in a direction from the distal end 42 towards the proximalend 40 of stem member 16 to form at least two expandable tine members46. Preferably, the at least one slot 44 has a length in the range of 4to 10 cm. It is contemplated that more than one slot may be used to formmore than two tine members.

The prosthesis further includes a central bore 34, coaxial withlongitudinal axis 48, which has proximal and distal ends 35, 36. Thebore 34 extends longitudinally from within the mounting cavity 30 andmerges into a tapered open tine cavity 38. Preferably, the bore 34maintains a uniform diameter in the range of 4 to 9 mm, which should beless than the diameter of open tine cavity 38. In an exemplaryembodiment, tine cavity 38 has a conical taper with a diameter whichranges from 6 to 14 mm at one end proximate the distal end 36 of bore 34and 8 to 18 mm proximate the distal end 42 of stem member 16. Theconical bore 34 generally has an initial diameter which is less than aminor diameter of expander nut 20 and a diameter at the distal end 42greater than or equal to a major diameter of expander nut 20, asdiscussed in more detail later herein.

Referring to FIGS. 2 through 4B, the system 10 further includes anelongate bolt member 18 having a proximal end 52 and a distal end 54.The bolt member 18 includes a head portion 50 and a shaft portion 55that extends distally from the head portion 50. The shaft portion 55preferably includes both an unthreaded shaft portion 56 disposedadjacent to the head portion 50, and a lower, threaded portion 58disposed adjacent to the unthreaded portion 56. The unthreaded shaftportion 56 preferably has an outer diameter that is less than the outerdiameter of the head portion 50. The lower, threaded portion 58preferably has a diameter less than or equal to the diameter of theunthreaded portion 56. The bolt member 18 is disposable within bore 34of stem member 16 in the manner discussed below.

The bolt member 18 is illustrated with a bolt head opening 51 having sixflattened sides suitable for engaging a hex allen-type wrench. However,the bolt head 50 can be provided with other configurations known tothose having ordinary skill in the art to permit the bolt member 18 tobe tightened or loosened with a tool or by hand when coupled to theexpander nut 20.

Referring to FIGS. 2-5B, the expander nut 20 includes a superior surface60 and an inferior surface 62 with a threaded center bore 64 extendingfrom the superior surface 60 to the inferior surface 62. When properlypositioned in the prothesis, the threaded center bore 64 is coaxial withthe longitudinal axis 48 of stem member 16. The expander nut 20 furtherincludes at least one anti-rotation means or rotation inhibitingprojection 66 and at least one pair of opposed tine engaging side walls68 adjacent to the at least one rotation inhibiting projection 66. Thetine engaging sidewalls 68 are adapted to matingly engage an innermating surface 47 of tine members 46 when the expander nut 20 isthreadably mated to the bolt member 18. In one embodiment, the tineengaging sidewalls 68 may be slightly curved in the longitudinaldirection to promote smooth contact with the inner mating surface 47 oftine members 46. In operation, the tine engaging sidewalls 68 cooperatewith the rotation inhibiting projection 66 to expand tine members 46when bolt member 18 is turned.

In an exemplary embodiment, the components of the prosthesis system canbe assembled in the following manner. The bolt member 18 is firstpositioned, distal end first, into mounting cavity 30 and positionedsuch that the head portion 50 is recessed within the cavity 30 and thebolt shaft 55 extends into bore 34. The expander nut 20 then ispositioned proximate the distal end 42 of stem member 16 and therotating inhibiting projections 66 are aligned with slots 44 on the stemmember 16. The expander nut 20 and bolt member 18 are then joined bymechanical interaction of the threads of bolt shaft 55 with the centerbore 64 of expander nut 20 to form a secure prosthesis assembly. Asassembled, the prosthesis system may now be implanted in a patient andexpanded to a desired configuration.

Referring to FIGS. 4A, 4B, 5A and 5B, the rotation of the bolt member 18in a first direction, typically clockwise, is effective to draw or urgethe expander nut 20 towards the proximal end 40 of stem member 16. Asthe bolt member 18 is rotated, the tine engaging sidewalls 68 arebrought into contact with inner mating surface 47 of tine members 46. Asthe expander nut 20 is urged upwardly in the tapered tine cavity 38,engaging sidewalls 68 press against the inner mating surfaces 47 causingtine members 46 to be pushed outwardly in a direction generallytransverse to the longitudinal axis 48 of stem member 16. The prosthesismay be further adjusted by either tightening or loosening bolt member18, thereby enabling the expander nut 20 to move longitudinally in adirection towards or away from the proximal end 40 of the stem member16.

In an unexpanded condition as shown in FIGS. 4A and 5A, the prosthesiscan be first passed through a narrow section of bone, such as theisthmus of a femur. Once the prosthesis is inserted past the isthmus,the bolt member may be turned to expand the tine members to fill thebone area where the supporting cortical bone is diverging. Once thedesired expansion of the prosthesis is achieved, the prosthesis will besecured in place in the long bone.

In the embodiment shown in FIGS. 5A and 5B, the prosthesis includes anexpander nut 20 having more than one diameter effective to spreadadjacent tine members in a non-uniform fashion with respect to oneanother. The expander nut 20 includes a minor diameter 74, measured in afirst direction, which is preferably in the range of about 8 to 16 mm.The expander nut 20 also includes a major diameter 76, measured in asecond direction substantially transverse to the minor diameter 74,which is preferably in the range of about 10 to 18 mm. As so configured,the tine members which are positioned about the major diameter 76 can beexpanded to a greater relative distance than the tine members which arepositioned about the minor diameter 74.

An alternate embodiment of the prosthesis system 10 is shown in FIGS. 6Aand 6B. In this embodiment, the expander nut 80 includes opposed pairsof rotation inhibiting projections 82 and tine engaging sidewalls 84.The rotation inhibiting projections 82 are adapted to engagelongitudinal slots provided on the stem member to prevent unwantedrotation of the expander nut. The expander nut 80 further includes athreaded central bore 88 for mating with a bolt member effective to drawthe expander nut towards the proximal end of the prosthesis. In theembodiment shown in FIGS. 6A and 6B, as the bolt member is turned, thetine members 90 are expanded in a uniform fashion with respect to oneanother.

Alternatively, as shown in FIG. 7, the prosthesis may be provided withtine members that have varying thicknesses. In this embodiment, theprosthesis includes an expander nut 98 and tine members 100, 102, 104and 106 of varying thicknesses. As illustrated, tine members 100 and 102are provided with thicker cross sections relative to tine members 104and 106, forming a prosthesis with more than one effective diameter. Theprosthesis includes a first, minor diameter 112, measured in a firstdirection about tine members 104 and 106. The first, minor diameter ispreferably in the range of about 10 to 18 mm. A second, major diameter114, is measured in a second direction substantially transverse to thefirst diameter 112 about tine members 100 and 102. The second, majordiameter is preferably in the range of 13 to 23 mm. In thisconfiguration, tine members 100 and 102 will be expanded, upon turningof a bolt member coupled to central bore 110, to a larger diameterrelative to tine members 104 and 106. The thickness of the individualtine members in the minor diameter may range from 1 to 3 mm. Thethickness of the individual tine members in the major diameter may rangefrom about 2 to 6 mm.

It is understood that various modifications can be made to the presentinvention without departing from the intended scope thereof. Theentirety of all references noted herein is expressly incorporated byreference herein.

What is claimed is:
 1. A surgical system comprising: an implantableelongate hollow stem member having a proximal end including a jointmotion surface adapted to receive a joint articulation member and adistal end having at least two expandable tines formed therein, the atleast two tines extending along at least a portion of the stem member ina direction from the distal end towards the proximal end, each tinehaving a cross-sectional thickness wherein at least one of the tines hasa thickness different than the thickness of another tine; and anexpander nut disposed at a distal end of the stem member, between thetines, such that the expander nut is movable towards the proximal end ofthe stem to separate the tines, the expander nut including one or moresidewall projections adapted to extend between the tines for engagingthe stem member to prevent rotation of the expander nut.
 2. The surgicalsystem of claim 1, wherein the expander nut includes a minor diameter,measured in a first direction, in the range of 10 to 18 mm.
 3. Thesurgical system of claim 2, wherein the expander nut includes a majordiameter, measured in a second direction substantially transverse to theminor diameter, in the range of 13 to 23 mm.
 4. The surgical system ofclaim 1, wherein distal end of the elongate hollow stem has fourexpandable tines.
 5. The surgical system of claim 4, wherein theexpander nut includes four sidewall projections, each sidewallprojection being adapted to extend between two expandable tines.
 6. Thesurgical system of claim 1, further comprising a bolt member disposablewithin the elongate hollow stem member, the bolt member having aproximal end and a distal end, wherein at least a portion of the boltmember proximate the distal end is threaded.
 7. The surgical system ofclaim 6, wherein the expander nut is threadably matable with the distalend of the bolt member such that rotation of the bolt member in a firstdirection is effective to draw the expander nut towards the proximal endof the stem member to separate the tines.
 8. The surgical system ofclaim 7, wherein the expander nut includes a threaded center bore thatis coaxial with a longitudinal axis of the stem and is threadablymatable with the distal end of the bolt member.
 9. The surgical systemof claim 1, wherein the elongate hollow stem members includes at leastone surface feature formed on an outer surface of at least one of theexpandable tines.